Back in the fourth century B.C. Rome was an incipient Republic, compressed in the center of the Italian peninsula, whose only alternative for growth was to absorb all those peoples that surrounded it in its expansion. Etruscans, Samnites, Aequi and Volcans ended during that time under the Roman yoke. In the year 391 B.C. Rome maintained a tense, and at times belligerent, situation with its northern neighbor, Etruria.
A few years ago a Gallic tribe had crossed the Alps, the Senones to be more specific, commanded by a peculiar individual, King Breno , the only chief of Celtic tribes who managed to wear a crown in Gaul before Vercingetorix. They settled in the area that was later renamed Galia Cisalpina (the current Po valley) removing from there the Umbrians who inhabited those lands. Brennos's ambition was not content with this new territory. That same year, seeing the weakness of the neighborhood and the possibility of getting a quick and large booty, the Senones attacked Etruria, besieging the city of Clusium (Chiusi, in Tuscany) The Etruscans, weighing the lesser evil between the two fearsome forces that imprisoned them, asked Rome for help, help that arrived in time. The trigger of the hostilities between Gauls and Romans was Quintus Fabius , one of those sent by Rome, who killed one of the Gallic leaders during the negotiations. This vile Roman meddling, and the complete absence of retaliation for such insult by the Senate, so angered King Brennus that, feeling insulted, he broke up his camp and stood before Rome.
The City did not have any energetic man at the head of its legions at that time. The only one capable of stopping Breno, Marco Furio Camilo , was absent, voluntarily exiled in Ardea after being accused by the tribune of the plebs Lucius Apuleius of embezzling funds from the immense booty obtained after the surrender of the Etruscan city of Veii. According to tradition, on July 18, 390 B.C. the Gauls massacred the Roman troops commanded by Quintus Sulpicius in the battle of the Alia river, very close to Rome. The survivors of that disaster arrived in Rome in a panic, climbing towards the Palatine without thinking of closing the gates. Thanks to such negligence, the Gauls entered the streets of Rome with blood and fire. Almost all the documentation prior to this day was lost forever, devoured by fire and barbarism.
The remnants of the militia and the citizens who were able to escape the looters took refuge in the Capitol, the acropolis of ancient Rome, while the Gauls thoroughly looted the rest of the city. The Curia, thanks to the double prowess of an intrepid messenger, demanded that Camilo intervene because he considered the former dictator the only military man capable of getting the Gauls out of Rome. Legend has it that the Romans thwarted a Gallic attack on the Capitol thanks to the warning of the geese from the temple of Juno, since that day a sacred animal, thus waking up the guard that prevented the Capitol from being taken. Camilo only agreed to return to the city if it was the people who requested it and ratified him again as dictator. And so it was.
Camilo reorganized the fugitives and scattered troops and, with the help of his magister equitum Lucius Valerio , he surprised and surrounded the unsuspecting Gauls. Brenno, seeing himself trapped by the resistance of the Capitol and Camilo's army, without food after several months of siege and surrounded by destruction and misery, agreed to agree to a ransom to liberate the city. Here history mixes with legend. Supposedly, the Gallic king tricked the weights that would measure the ransom payment, one thousand pounds of gold (approximately 327 kg). Some of the parliamentarians in the Capitol must have noticed this and reproached him for cheating on him. Brenno, furious, threw his sword on the scales and responded with the famous phrase “Vae Victis! ” (Woe to the vanquished!)
Camilo, not at all satisfied with agreeing to pay that ransom, as plenipotentiary dictator disavowed the deal and answered Breno with another famous phrase:“Non aurum sed ferrum liberanda patria est ” (It is with iron, not with gold, that the country is liberated). Marco Furio Camilo crushed the Gauls days later and triumphantly entered Rome, being hailed as pater patriae and conditor alter urbis (father of the country and second founder of the city)
The bitter day of July 18 was marked in Roman citizenship for generations. Every anniversary of the looting, the Capitol's guard dogs were crucified as punishment for their neglect. Those executions had special spectators. The geese from the temple of Juno, the only ones that alerted the people of the Gallic attack, were brought in front of the crosses and perched on purple cushions...
Source:Archenemies of Rome